The invention relates to improvements in apparatus for controlling the movement of a door panel or an analogous (normally pivotable) component between first and second positions, especially between closed and open positions. More particularly, the invention relates to improvements in door closers of the type disclosed in the commonly owned U.S. Pat. No. 4,937,913.
The copending patent application describes and shows a door closer wherein an elongated housing confines a reciprocable damping piston which divides the internal space of the housing into a first and a second compartment. The first compartment contains one or more springs which bias the piston to a position corresponding to the closed position of the door panel. The internal space of the housing is filled with a fluid, and the housing has a channel which establishes a path for the flow of fluid from the first compartment into the second compartment when the door panel is pivoted from open position. The arrangement is such that the flow of fluid by way of the channel is reduced or interrupted when the piston reaches a certain axial position, i.e., when the door panel has completed a predetermined angular movement from closed position. In order to permit further pivoting of the door panel toward fully open position, the piston and/or a check valve therein defines at least one bypass which establishes a relatively small path for the flow of fluid from the first compartment into the second compartment during that stage of pivotal movement of the door panel from closed position when the channel is already sealed or the rate of flow of fluid through the channel is greatly reduced. The purpose of the check valve is to permit the fluid to flow from the second compartment back into the first compartment while the spring or springs in the first compartment are free to dissipate energy and to pivot the door panel back to closed position. The connection between the piston and the door panel includes a shaft which is rotatably mounted in the housing, a rack and pinion drive between the shaft and the piston, and one or more levers, arms or other motion transmitting parts between the shaft and the door panel. The cross-sectional area of the bypass between the two compartments increases in a direction from the first compartment toward the second compartment. This is intended to prevent excessive rise of fluid pressure at the inlet of the bypass. The copending patent application discloses the possibility of providing the bypass in the peripheral surface of the piston or in the peripheral surface of the body of the check valve.
The door closer which is disclosed in the copending patent application operates quite satisfactorily as long as the fluid which is confined in the housing is free of solid impurities. However, the damping action is likely to be changed as soon as a solid impurity penetrates into and remains lodged in the bypass. Moreover, once the bypass is partially or completely blocked, the likelihood that the entrapped impurity or impurities would be flushed out by the fluid is very remote. Still further, the dimensions of the bypass must be selected with a very high degree of precision irrespective of whether the bypass is provided in the peripheral surface of the piston or in the peripheral surface of the body of the check valve which is installed in the piston. The impurities in the confined fluid can constitute particles of material which was removed from the housing, from the piston and/or from the check valve during manufacturing of the respective parts. Still further, the cross-sectional area of the bypass is likely to change during installation of the check valve in the piston and/or during installation of the piston in the housing.